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Old 07-31-2018, 12:04 AM   #1
87Skier
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Harsh 1-2 shift in rebuild 4L60E

I just finished rebuilding my first transmission and everything seems good except for the 1-2 shift. Even at very light throttle it still gives you a good jolt.

I picked up the vehicle knowing that the transmission was bad. Fluid was burnt, no Reverse, 2nd or 4th. It is in a 2000 Tahoe, and was original as far as I can tell. Transmission code is "0KCD".

Here's what was done:
Borg warner clutches
New steels
New band
Sonnax smartshell
New sungear for smartshell
Sonnax performance pack (pinless accumulators, line booster, didn't modify the PWM TCC)
Torlon checkballs
Transgo separator plate
Reused ORIGINAL SERVOS - NO CORVETTE SERVO
New pump
New torque converter
New bearings
New bushings

The only thing I'm not entirely confident in on this build is servo pin length. I seemed to get some mixed readings and ended up leaving it alone since it is fairly easy to change out in the vehicle.

Is there anyway to soften up the 1-2 shift feel? I don't mind a firm shift but this is far too harsh. Will modifying the tune soften the shift?

Thanks!
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1989 Chevy Suburban V2500 350/Turbo 400/4.11 gears
1996 Chevy Suburban K1500 350/4L60E
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Old 07-31-2018, 09:40 PM   #2
Bigdav160
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Re: Harsh 1-2 shift in rebuild 4L60E

Shift kit? Servo change? Didn't forget a check ball?

The first thing to check would be the 1-2 accumulator. Make sure the bore is smooth, seal and piston are in good shape.
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Old 08-01-2018, 02:43 PM   #3
YoungPup1977
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Re: Harsh 1-2 shift in rebuild 4L60E

Any time you “rebuild” a 4L60E and you do not install a shift kit you are asking for additional work. Work that should of been done the first time..... By boosting line pressure only, what do you think it’s going to do to the stock calibrated VB.
A transgo shift kit would be a requirement to say the least. It only cost 49 bucks. This shift kit fixes lots of 4L60e issues: P1870 code / brutal 1-2 shift / converter shudder / pump slide bounce that wears your pump out
When line pressure is increased you must match the accumulator to ECM, by the 2nd servo piston and the accumulator code found on the housing to install the correct spring. See pic

You bought a new separator plate most likely because a checkball wore almost all the way thru the plate but don’t stop there, you need to drill the new plate as required.

I suggest for installation of a transgo shift kit and once that is done than you can jump all over your tuning. MAF etc etc........
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Old 08-02-2018, 02:59 PM   #4
87Skier
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Re: Harsh 1-2 shift in rebuild 4L60E

It has stock servo's. All the checkballs are in the right place and none are missing.

I installed a shift kit during the rebuild: https://www.sonnax.com/parts/2928-performance-pack. Here's what Sonnax says the kit does:

"All components work together to carefully tune line pressure, accumulator pressure and shift calibration. It’s the ultimate way to get an impressive transmission that responds to throttle and increased load with quick, firm shifts."

Parts list:
  • 1-2 Accumulator valve shim
  • TCC pressure limiter valve (not installed in this trans)
  • 0.490" Boost valve
  • Elevated pressure return spring
  • High rpm pump slide spring
  • 4th servo return spring
  • Servo cushion spring
  • Servo piston D-Ring kit
  • 3-4 Accumulator piston kit
  • 3-4 Accumulator spring
  • Servo release check valve
  • Forward accumulator kit
  • Checkballs
  • Drill bits
  • 1-2 Pinless accumulator
  • 1-2 Accumulator inner spring
  • 1-2 Accumulator outer spring
  • 1-2 Accumulator waved spring

Separator plate was replaced because of the potential problems with stuck checkballs. None were noted as being stuck.
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1972 GMC Jimmy Custom 4.8L (L20)/6L90E/NP205
1989 Chevy Suburban V2500 350/Turbo 400/4.11 gears
1996 Chevy Suburban K1500 350/4L60E
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Old 08-02-2018, 06:08 PM   #5
YoungPup1977
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Re: Harsh 1-2 shift in rebuild 4L60E

So can you tell me why it’s shifting hard into 2nd ? What’s the difference from transgo shift kit and the performance pack you bought ? If you did everything you wanted to do than I can’t help you.
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